This invention relates to the treatment of blood, and more particularly to systems and implantable devices providing direct access to the vascular system of a patient receiving extracorporeal blood treatment.
The extracorporeal treatment of blood requires that the vascular system of a subject be directly accessed, and often accessed repeatedly. Such treatments include the removal of various components or toxins, and the addition of oxygen to the blood.
For example, hemapheresis is a treatment which involves the collection of blood cells, the removal of a specific blood cell type from the blood, or plasma exchange. It requires that the vascular system be tapped with, for example, a needle attached to a catheter. The blood is then circulated through an extracorporeal separating device, and then returned to the vascular system via a second needle stick. Hemapheresis may be performed once or repeatedly providing that adequate time is allowed for replacement of the blood cell by the donor's bone marrow.
Another blood treatment is hemodialysis, or the removal of various chemical substances from the blood. Such substances include ingested or injected drugs, or toxins created during normal body metabolism, the presence of which is most often due to renal impairment. Typically this treatment involves accessing the vascular system, connecting the vasculature to a hemodialysis pump and filtration mechanism, and returning the cleansed blood to the vascular system.
Accessing the vascular system may be achieved by temporary or permanent means, depending on the requirements of the patient. For example, methods are available to establish temporary access involving the percutaneous insertion of a single or double lumen cannula into a large vein such as the subclavian, femoral, or internal jugular.
However, to provide more adequately for the chronic renal impaired patient, it is preferable to surgically rearrange the peripheral vasculature, thereby creating a permanent access. The procedure usually involves connecting a large surface peripheral vein to an artery producing a fistula, or surgically creating a loop between an artery and a vein using a synthetic material such as expanded PTFE. The natural fistula, normally constructed from a vein or venous graft, is preferred over the synthetic loop which is prone to complications such as infections, clotting, and leakage. In either case, the surgery involved in its creation is a lengthy process, and maintaining the resulting reconstruction of the vasculature is a chronic problem. The fistula must mature or become arterialized before it can be accessed with the needles. Then, when it becomes functional, a number of complications may arise including clotting, thrombosis, infection, and infiltration of scar-forming cells. In addition, because hemodialysis is a chronic treatment, the required and repeated needle punctures eventually weaken and destroy the arterialized vein, which, to begin with, is abnormally pressurized and particularly susceptible to collapse.
Cleansing of the blood alternatively may be conducted by peritoneal dialysis, a treatment which does not necessitate accessing the vascular system. Peritoneal dialysis involves placing a dialysate solution into the peritoneal cavity of a patient via a catheter. The catheter is surgically implanted such that one end is secured within the cavity and the other end is accessible by either projecting through the skin or can be accessed subcutaneously (see for example, U.S. Pat. No. 4,490,137). The dialysate is allowed to remain in the cavity for a predetermined time to allow blood metabolites or toxins (solutes) to cross the highly vascularized peritoneal membrane and enter into the dialysate. The toxin-laden dialysate is later removed through the same catheter.
However, peritoneal dialysis may not be as desirable as hemodialysis because it rids the blood of metabolities indirectly using the peritoneal membrane as a filter and in fact, only 15% of patients currently receiving blood dialysis therapy undergo peritoneal dialysis.
Implantable and extracorporeal devices are known for the infusion of medicines and drugs into the vasculature (see, e.g., U.S. Pat. Nos. 4,673,394, 4,704,103, 4,692,146, and 4,014,328). However, such devices are not useful for extracorporeal blood treatments, as their construction does not take into account the fragile nature of blood elements which are highly susceptible to breakage, or hemolysis during transfer, intrinsic clotting, and immune response.
The implantable vascular access port disclosed in U.S. Pat. No. 4,673,394 includes a housing portion having a substantially right circular cylinder shaped, open-faced internal chamber, and a septum spanning the open face of the chamber to establish a closed reservoir. A cylindrical, tubular cannula extends from the sidewall of the chamber for coupling the reservoir to an external catheter. With such a configuration, the chamber and cannula geometries are ill-suited for the transfer of blood elements through the access port, particularly at the flow rates and pressures that are required for current hemodialysis techniques. As blood is transferred through the septum and injected into the chamber, flow patterns are established which include "dead flow" pockets, particularly in the corners of the chamber. Blood cells which enter these pockets merely circulate therein or hardly move at all, and never, or only after a long time, enter the flow through the cannula. Such movement or lack thereof increases the chances of coagulation of the blood. Further, at the relatively high flow rates, cell-lysing collisions occur at the abrupt interface of the chamber and the cannula. Such collisions are both from cell-to-cell interactions within regions of turbulence and from the physical impact of cells within the chamber sidewalls.
Therefore, it is an object of the present invention to provide an improved method of accessing the vascular system which is antiseptic, less traumatic to the patient, and which has potential for self-access or home care.
It is another object of the invention to provide an easier, quicker method of providing a vascular access which will not require maturation before it can be used for various extracorporeal blood treatments.
It is also an object to provide an improved vascular access device which can be reliably and repeatedly connected to an extracorporeal blood treatment, and which is durable and easy to use.